Many types of data transmissions have emerged that require certain transmission quality levels to maintain the integrity of the data when the data is transmitted over packet-switched networks (e.g., internet protocol networks). Video-on-demand and voice services are examples of such data transmissions. Voice services over internet protocol networks, commonly referred to as VoIP, are an emerging alternative to standard voice services over circuit-switched telephone networks, largely because of the potential cost savings provided by VoIP. By using packet-switched networks (e.g., the Internet) to transmit voice services, callers are able to avoid long distance fees associated with using a telephone carrier's traditional circuit-switched telephony networks.
However, implementation of VoIP has proved to be a challenging task with respect to providing the same voice quality typically offered by traditional circuit-switched telephone services. One aspect that makes high-quality VoIP a challenging task is congestion of internet protocol (IP) networks. When IP networks become congested, data transmissions experience longer transmission delays that may not meet minimum quality standards. Moreover, when IP networks are used to transport different types of data (e.g., voice transmissions and more typical types of digital data), chances of congestion increase, especially when minimum quality standards are required for more than one particular data transmission over the network.
Further, the common use of IP networks for transmitting various types of data, as well as associated control signaling, tends to complicate timing issues for data transmissions. Not only does control signaling require responses to messages within pre-specified time intervals, as mentioned above, time-criticalness is also required for many types of media data traffic transmissions (e.g., video-on-demand and voice services transmissions). The wide variety of timing requirements for the different types of transmissions tends to complicate network timing, which can undesirably affect the quality of transmissions that have minimum quality standards. In particular, excessive packet loss, transmission delay, or variation in transmission delays (i.e., jitter) may degrade the quality of transmitted data signals, including voice services transmissions. Moreover, bandwidth limitations, lengths of network paths, and other network parameters may also undesirably affect the quality of data transmissions over IP networks.
Parameters used to define and measure the quality of data transmissions over IP networks are commonly referred to as quality-of-service (QoS) parameters, which include parameters such as packet loss, delay, and jitter. To help control QoS parameters for data transmissions, many traditional VoIP services have implemented admission controls for selecting which data transmissions (e.g., which telephone calls) to admit for transmission over the IP network based on a predefined order of priority. If, for example, the IP network cannot handle additional telephone calls of lower priority than the already admitted telephone calls, the call admission controls will not admit the additional telephone calls for transmission over the IP network. While call admission controls have helped to prevent instances of voice quality degradation by preventing congestion of IP networks, call admission controls have several drawbacks. For example, when call admission controls are relied upon solely or primarily to maintain voice quality parameters, customer satisfaction is often jeopardized whenever callers are unable to place calls due to a lack of network availability. The inability to place calls can easily cause would-be callers to feel dissatisfied with the VoIP services offered by service carriers. In turn, the users' unsatisfactory experiences may cause service carriers to suffer a loss of business, reputation, or goodwill.
In short, conventional IP networks do not transmit data in a manner that consistently satisfies minimum quality standards required by many types of data transmissions (e.g., voice services transmissions).